FIELD OF INVENTION:

The present invention relates to an environmentally benign biodegradable polymer and process of preparation thereof. More specifically, the invention relates to group 4 metal aryloxy compounds as polymerization catalyst, in lactide polymerization.

BACKGROUND OF THE INVENTION:

Synthetic petrochemical-based polymers have had a tremendous industrial impact since the 1940s. Despite the numerous advantages of these materials, two major drawbacks remain to be solved, namely, the use of nonrenewable resources in their production and the ultimate fate of these large-scale commodity polymers. Due to their unique properties, biodegradable polymers have long been considered as alternative environmentally friendly polymers, and the spectacular advances achieved over the last 30 years in the synthesis, manufacture, and processing of these materials have given rise to a broad range of practical applications from packaging to more sophisticated biomedical devices. Of the variety of biodegradable polymers known, linear aliphatic polyesters are particularly attractive and most used. Notably these polymers are not only biodegradable (the aliphatic polyester backbone is intrinsically sensitive to water and heat) but also bioassimilable, since their hydrolysis in physiological media gives nontoxic components that are eliminated via the Krebs cycle as water and carbon dioxide. Furthermore, the influence of the rheological and physical characteristics of these polymers should not be underestimated. Spectacular variations in physical properties can also be achieved during the polymer processing itself, through orientation, blending, branching, cross-linking, or plasticization. Indeed, these biodegradable polymers may well offer a practical solution to the ecological problems associated with bioresistant wastes. Flexible films, rigid containers, drink cups, and bottles are representative products already available in the marketplace. Numerous medical applications have also been considered for both surgical and pharmacological use. Historically, the use of synthetic biodegradable polymers as sutures started in the 1970s, the most widely used bioassimilable sutures being Dexon and Vicryl. Besides tissue repairing and engineering, biodegradable implants have also been used for fixation of fractured bones and joints. Accordingly, several orthopedic devices are commercially available such as the ligating clips and bone pins produced. With these biodegradable and bioassimilable devices, there are no particular precautions necessary for their use and no need for a removal operation, which is highly advantageous compared with metal implants. One of the many methods in synthesizing these polymers is the ring opening polymerization of the corresponding cyclic lactone monomers or lactide (LA).

RING OPENING POLYMERIZATION
Many catalyst systems have been evaluated for the polymerization of lactide and lactones including complexes of aluminum, zinc, tin, and lanthanides. Even strong bases such as metal alkoxides have been used with some success. Depending on the catalyst system and reaction conditions, almost all conceivable mechanisms have been proposed to explain the kinetics, side reactions, and nature of the end groups observed in these polymerizations. Tin compounds, especially tin(ll) bis-2-ethylhexanoic acid (tin octoate), are preferred for the bulk polymerization due to their solubility in molten state, high catalytic activity, and low rate of racemization of the polymer. Conversions of 90% and less than 1% racemization can be obtained while providing polymer with high molecular weight. The polymerization of lactide and lactones using tin octoate is generally thought to occur via a coordination-insertion mechanism. High molecular weight polymer, good reaction rate, and low levels of racemization are observed with tin octoate-catalyzed polymerization. Typical conditions for polymerization are 180±210 °C, tin octoate concentrations of 100±1000 ppm, and 2±5 h to reach ca. 95% conversion. The polymerization is first order in both catalyst and monomer. Frequently hydroxyl-containing initiators such as 1-octanol are used to both control molecular weight and accelerate the reaction. Copolymers of lactide with other cyclic monomers such as caprolactone can be prepared using similar reaction conditions. These monomers can be used to prepare random copolymers or block polymers because of the end growth polymerization mechanism. The coordination-insertion ring opening mode of polymerization is the most popular because of its capability in producing polymers with narrow molecular weight distribution. A large variety of metal complexes containing alkyl, alkoxide, carboxylates and oxides have been reported to possess good activity. Tin alkoxides being the most popular route often envisages initiators of the composition Sn(OR)2.

Other metal alkoxides or aryloxides containing aluminum, lithium, titanium and some lanthanides have been reported. A plethora of bio-compatible metal based initiators have also been reported recently. These include examples from zinc, magnesium and calcium. In the 1980s, calcium ammoniate was popularly used for the ring opening polymerization of £-caprolactone. Extreme hydrolytic sensitivity and limited solubility in organic solvents restricted its use. Key issue in commercialization is the catalyst residue. In spite of the versatile applications of Lewis acids in organic synthesis, their use in polymer chemistry has been quite limited. In the recent years, the increasing need to search alternative polymeric materials to those based on non¬renewable petroleum resources, along with the desire to produce environmentally benign biodegradable plastics has provided active impetus towards the polymerization of cyclic esters. Aliphatic polyesters have been implicated for biomedical applications such as delivery medium for the controlled release of drugs and biodegradable surgical sutures. Polylactic acid has potential utility for such usage as a result of their permeability, biocompatibility and biodegradability. One of the convenient strategies in synthesizing these polymers is the ring opening polymerization of lactide monomer. Although a multitude of initiators are known for such polymerizations, the major hurdle regarding the commercialization of such processes is the difficulty in removing catalyst residues and the cytotoxicity associated with such residues, which limit the application of these polymers in biomedical applications.

PRIOR ART:
The popular methodology of catalyst construction commonly employs a rigid, polydentate ancillary ligand around the metal center with one or more pendant initiating groups. The ligand has a profound influence on the catalyst nuclearity and shows an impact on the coordination-insertion growth mechanism. Initiators with Group 4 metals have been popular as they exhibit reasonable control on the polymerization process. Initiators with a ligating back bone containing chiral phenoxyimine,1 tris(phenoxy)amine,2 bis(/3-ketoamidate),3 bis(iminophenoxy),4'5 N-heterocyclic carbene,6 bis(phenoxy)amine,7"9 pyrrolylamine,10 tris(alkoxy),11,12 tris(alkoxy)amine,13"15 bis(amido),16 chalcogen-bridged bis(aryloxy)17 and methylene-bridged bis(phenoxy)18 derivatives. In addition, there are reports employing titanium

n-butoxide and zirconium n-propoxide19 and titanium phenoxide20 as initiators. A titanium alkoxide based metal organic framework was recently reported to possess activity for such processes.21 The use of metallocene ester enolates for the polymerization of lactide is reported.22 The polymerization of lactide using Ti and Zr complexes of phenylenediamine bis(phenolate) ligand23 and sulphonamide supported backbone have been reported recently.24 Ti complex of isoquinolinyl-naptholate25 and Zr complex of trans-substituted diamido/diamine cyclam are reported to be active for CL polymerization.26 The polymerizations described from such initiators have exclusively relied upon the coordination-insertion mechanism. The initiation process is rapid and there is minimal chance of unwanted transesterification. In case of polymerization of cyclic esters, there is no systematic correlation between the structural features of the ancillary ligand and polymerization characteristics. The ease with which the acyl oxygen bond of the cyclic ester monomer cleaves depends on the electron environment provided by the initiating group (most often as an alkoxy fragment) contained in the initiator.
Hence the precise role of the ancillary ligand is not very justified for the polymerization of cyclic esters which propagate in a non stereospecific manner. Logically, such polymerizations should proceed in the desired manner by controlling the electronic environment around the metal alkoxy fragment. An alternative approach to the polymerization of cyclic esters is the activated monomer mechanism27"31 whose practical utility has not been substantially investigated as compared to the coordination-insertion mechanism. None of the initiators derived from the above ligand backbone have been investigated in this regard. A reason that may be attributed to this observation is the use of intolerable protic initiators along with these organometallic compounds as catalysts. Hence, there are possibilities of loss of catalyst identity during the polymerization process. The recent results of the inventors indicate that iron and ruthenium chloride catalysts in the presence of protic initiators like alcohols produce comparable or better results for e-caprolactone (CL) and 5-valerolactone (VL), using the activated monomer mechanism,32 as compared to the ones reported for alkoxide initiators containing bulky ligands where the polymerization proceeds by the coordination-insertion mechanism. Using such a methodology, much shorter polymerization time, far higher Mn and low MWDs were observed. This proved that elaborate ligands may not be an absolute necessary requirement in the development of such a technology involving the polymerization of cyclic ester monomers.

US 6214967 discloses a two-step process for the polymerization of lactide to polylactide, a biodegradable polymer, in which the first step polymerization is carried out to a conversion of at least 50% by weight, and in the latter step the polylactide is polymerized further to a high conversion in conditions in which the mixing of the melt and the evaporation of the lactide are avoided. Conventional initiators suitable for lactide polymerization, such as various tin and iron compounds, were used in the polymerization.

US 5235031 discloses a process for polymerizing lactide and up to 20 mole percent of another lactone in the absence of solvent at 100° to 220° C. using an yttrium or lanthanide series rare earth metal catalyst.

US 6376643 discloses a method of polymerization of lactide or glycolide (GA) monomers and in particular to a method of polymerizing one type of the monomers or two types of the monomers using alkyl aluminum catalyst to proceed with bulk or solution polymerization to prepare biodegradable homopolymers or copolymers, and high-molecular-weight homopolymers of polylactide (PLA), polyglycolide (PGA), or copolymers of lactide/glycolide prepared thereof.

US 5357034 disclose a continuous process to produce high molecular weight polylactic acid from lactic acid. The process of polymerization is carried out in the presence of a catalyst selected from the group consisting of tin metal, tin oxide and tin esters of C1-18 carboxylic acids.

European Polymer Journal 35(12) 1999, 2131-2138 discloses ring-opening homopolymerization and copolymerization of f-caprolactone and DL-lactide initiated with rare earth 2-methylphenyl samarium in bulk. The initiator can give high yield and high molecular weight polymer.

US 7026496 discloses diamido alkoxides as polymerization initiators in the polymerization of lactides

US 6166169 discloses an aliphatic polyester and/or copolyester, obtained from a polyreaction of at least one monomer from the group comprising lactides, lactones, cyclic carbonates and cyclic anhydrides with catalyst Sn-bis(2-ethylhexanoate) and co-catalyst P(Ph)3.

International Journal of Polymer ScienceVolume 2010 (2010), Article ID 490724, doi:10.1155/2010/490724 discloses Ring-Opening Polymerisation of rac-Lactide Using a Calix[4]arene-Based Titanium (IV) Complex.

US 20050009687 disclose caged titanium alkoxide as a catalysts for polymerization of cyclic esters such as Lactides.

GB2447269 disclose a catalyst comprising a complex formed from the reaction of a titanium, zirconium, hafnium or aluminium compound, selected from an alkoxide, a condensed alkoxide, a halide, haloalkoxide, amide or oxyhalide with a carbohydrate, such as a monosaccharide containing a 5- or 6- membered carbon chain or cyclic system or a disaccharide or polysaccharide based on a 5- or 6-membered carbon chain or cyclic system for the ring-opening polymerization of a cyclic organic compound.

All the above cited prior arts disclose various reaction conditions for the polymerization of lactides. The initiators/catalyst used in the polymerization reaction are inorganic complexes containing elaborate ligands which make the process complex and the key issue in commercialization is the catalyst residue and the cytotoxicity associated with such residue. Further the use of co-catalyst is also a must in some polymerization reaction to enhance the activity of the catalyst which is not economical and also removing of co-catalyst is cumbersome and laborious. Hence achieving good molecular weight polymer using a catalyst without having to retort to elaborate ligands and co-catalyst is an important need at this stage.

OBJECT OF THE INVENTION:
To over come the short comings of the prior art the main object of the present invention is to synthesis an environmentally benign biodegradable polymer from a corresponding monomer using mild Lewis acid as the catalyst

Another object of the present invention is to employ a catalyst without having resort to elaborate ligands for lactide polymerization.

Yet another object of the present invention is to employ a catalyst which is devoid of the problem relating to catalyst residue and the cytotoxicity associated with the residue for lactide polymerization.

Yet another object of the present invention is to employ a catalyst which does not require any co-catalyst for lactide polymerization.

Yet another object of the present invention is to employ a catalyst for lactide polymerization that has environmentally benign metals that are constituents in the mammalian anatomy so that the residues are potentially harmless.

Yet another object of the present invention is to synthesis group 4 metal aryloxy compounds as bulk polymerization catalysts for lactide polymerization.
Further object of the present invention is to employ the synthesized catalyst in the lactide polymerization to form environmentally benign biodegradable polymer.

SUMMARY OF THE INVENTION:
The invention relates to biodegradable polymers obtained by polymerizations of corresponding monomers such as /.-lactide (L-LA) or rac-lactide (rac-LA) with aryloxy compounds as catalyst in 200:1 molar ratio using solvent-free conditions (bulk polymerization) at 140 ° C to form environmentally benign biodegradable polymer, poly lactides. The catalyst for polymerization, used is Group 4 metal (Ti, Zr, Hf) aryloxy compounds which are synthesized from Ti(0-iPr)4, Zr(0-iPr)4(HO-iPr) or Hf(0-tBu)4 and several phenols having different substituents on the phenyl ring, in

1:4 stoichiometric ratio in toluene, employing the alcoholysis route. The synthesized aryloxy compounds have been characterized thoroughly by 1H and 13C NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and their purity has been assured by correct elemental analysis values.

BRIEF DESCRIPTION OF THE DRAWINGS:
Figure 1. depicts Molecular structure of catalyst 10. Thermal ellipsoids were drawn at 30 % probability level.
Figure2. depicts Plot of Mn vs [L-LA]o/[Cat]0 for L-LA polymerization using catalysts 3, 8 and 11
Figure 3. depicts Plot of Mn vs [rac-LA]0/[Cat]0 for rac-LA polymerization using catalysts 3, 8 and 11
Figure 4. depicts Homonuclear decoupled 1H NMR (400 MHz, CDCI3) spectrum of the methine region of heterotactic enriched PLA obtained using catalyst 3
Figure 5. depicts Homonuclear decoupled 1H NMR (400 MHz, CDCI3) spectrum of the methine region of heterotactic PLA obtained using catalyst 8
Figure 6. depicts Homonuclear decoupled 1H NMR (400 MHz, CDCI3) spectrum of the methine region of heterotactic PLA obtained using catalyst 11
Figure 7. depicts Semilogarithmic plots of L-LA conversion in time initiated by catalysts 3, 8 and 11: [L-LAy[Cat]0 = 1000 at 140°C

Figure 8. depicts Semilogarithmic plots of rac-LA conversion in time initiated by catalysts 3, 8 and 11: [rac-LA]o/[Cat]0 = 1000 at 140°C

Figure 9. depicts 1H NMR spectrum of the crude product obtained from a reaction between rac-LA and catalyst 2 in 20:1 ratio

Figure 10. depicts 1H NMR spectrum of the crude product obtained from a reaction between rac-LA and catalyst 8 in 20:1 ratio.

DETAILED DESCRIPTION OF THE INVENTION:
The present invention relates to a bio degradable polymer obtained from polymerization of corresponding monomer such as lactides with group 4 metal aryloxy compounds as catalyst. The invention also relates to a variety of Group 4 metal (Ti, Zr, Hf) aryloxy compounds for use as a catalyst in lactide polymerization. A variety of Group 4 metal (Ti, Zr, Hf) aryloxy compounds 1-11 were synthesized from Ti(0-/Pr)4, Zr(0-/Pr)4(HO-/Pr) and Hf(0-ffiu)4 and several phenols having different substituents on the phenyl ring, employing the alcoholysis route. These compounds were prepared by reacting Ti(0-/Pr)4, Zr(0-/Pr)4(HO-/Pr) and Hf(0-fBu)4 with the appropriate phenol in 1:4 stoichiometric ratio in toluene. Evaporation of the solvent afforded the crude product which was further purified by crystallization from toluene. These compounds were isolated as yellow to colorless solids in high yields and purity. Table 1 lists these compounds with appropriate legends.

Table 1. List of catalysts used is this study


The aforementioned compounds (1-11) have been characterized thoroughly by 1H and 13C NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS) and their purity has been assured by correct elemental analysis values. These compounds possess a dimeric structure in the solid state. This is proved from ESI-MS studies and single-crystal X-ray studies on 10 (Fig 1).

It was surmised that a variation of electronic environments of the phenyl ring constituting the -OAr moiety must have a consequence in such polymerizations. Polymerizations were performed with L-lactide (L-LA) and rac-lactide (rac-LA) monomers. Initials studies were performed with these monomers and compounds 1-11 in 200:1 molar ratio using solvent-free conditions (bulk polymerization) at 140 °C. The results are depicted in Tables 2 and 3 respectively.

Table 2. Results of L-LA polymerization using various aryloxy compounds in 200:1 ratio at 140 °C

a Time of polymerization measured by quenching the polymerization reaction when all monomer was found consumed. " Isolated yield. c Measured by GPC at 27 °C in THF relative to polystyrene standards with Mark-Houwink corrections for Mn.

Table 3. Results of rac-LA polymerization using various aryloxy compounds in 200:1 ratio at 140 °C

a Time of polymerization measured by quenching the polymerization reaction when all monomer was found consumed. b Isolated yield. c Measured by GPC at 27 °C in THF relative to polystyrene standards with Mark-Houwink corrections for Mn.
The results in Table 2 & 3 reveal that the aryloxy periphery indeed determines /Wn and MWD's. For highly electron withdrawing groups, there are chances of rapid trans-esterification reaction. There is a better control of MWD's descending down the group from Ti to Hf. The variations of Mn with [L-LA]o/[Cat]0 ratio using 3, 8 and 11 for L-LA polymerizations were studied. The plots are linear indicating that there is a continual rise in Mn with an increase in [L-LA]o/[Cat]0 ratio. Similar results were noticed for rac-LA polymerizations using these catalysts (Figs 2 and 3). Homonuclear decoupling 1H NMR studies reveal that the polymerization of rac-LA using Ti catalyst yields heterotactic enriched polymer (Fig 4) while using Zr and Hf catalyst leads to complete heterotactic enrichment (Figs 5 and 6).

The kinetic studies for the polymerization of L-LA and rac-LA using 3, 8 and 11 were studied. The kinetic studies for the polymerization of L-LA and rac-LA in ratio [LA]o/[Cat]0 = 1000 were performed at 140 °C. The results are depicted in Figs 7 and 8 respectively. The plots suggest that there is a first-order dependence of the rate of polymerization on monomer concentration. No induction period was observed. These plots exhibit linear variation. From the slope of the plots, the values of the apparent rate constant (/capp) for L-LA polymerizations initiated by 3, 8 and 11 were found to be 6.01 *10"2 min"1, 4.96 10"2 min"1 and 3.24 10'2 min"1 For rac-LA, the results are similar and the apparent rate constant (/capp) for polymerizations initiated by 3, 8 and 11 were found to be 5.17 10-2 min"1, 2.92*10"2 min"1 and 1.84 10"2 min"1. In general the rates are slower for rac-LA polymerization.

A convenient tool to gain insight into the polymerization mechanism using 1-11 is a thorough understanding of the polymer composition upon using these compounds as catalysts through 1H NMR spectroscopy. Compound 2 and 8 were selected as prototype representatives for compounds with alcohol coordination and without. Low molecular weight oligomers of poly(caprolactone) were synthesized by stirring rac-LA with 2 or 8 in 200:1 molar ratio under neat conditions at 140 °C. The product was washed with methanol. In all the cases, the residue after removal of methanol was analyzed using 1H NMR spectroscopy.

Using 2, the major product of the composition indicated in Fig 9. is formed as understood through the analysis of 1H NMR spectrum. This is an implication that coordinated /PrOH from the catalyst has an active role as the initiator and the polymerization proceeds through the activated monomer mechanism.

In case of 8, the major product as indicated in Fig 10 is seen from the 1H NMR spectrum. Here, the polymerization proceeds by the anticipated conventional coordination-insertion mechanism.

In summary, the alcoholysis route was utilized for synthesizing several new aryloxy compounds of group 4 metals. They are potent activators for the polymerization of L-LA and rac-LA. These results are based upon a simplified approach to the
polymerization of LA using mild Lewis acids as catalysts The methodology employed and the concepts reported may be considered crucial for bulk scale procedures. The achievement of obtaining good molecular weights without having to resort to elaborate ligands is a noted feature for the present system.

In one of the preferred embodiment the present invention relates to a process for synthesizing a high number average molecular weight Mn biodegradable polymer comprising reacting a corresponding monomer from the group of lactides with a catalyst of Group 4 metal aryloxy compounds (M)(0 C6R6)n(OH-R')m wherein M is a metal selected from group 4 of the periodic table , (R) is a first substituent selected from hydrogen, alkyl, halogens, trihalo alkyl; R' is a second substituent selected from alkyl group such as iso propyl and tertiary butyl group; n is a whole number ranging from 1-4; m is a whole number ranging from 0-1 wherein the feed ratio of the monomer to the catalyst is adjusted to achieve the desired molecular weight Mn of the polymer. As per the invention the feed ratio of monomer and the catalyst for is polymerization reaction is generally 200:1 molar ratio and the feed ratio of the monomer and the catalyst is varied to vary the molecular weight Mn of the polymer. In accordance with the invention the feed ratio of the monomer to the catalyst is increased to increase the molecular weight Mn of the polymer. As per the invention the number average molecular weight of the obtained bio degradable polymer is between 15.58 kg/mol and 135.77 kg/mol and molecular weight distribution is between 1.38 and 1.14.

In another preferred embodiment the present invention shall disclose a environmentally benign biodegradable polymer having a high number average molecular weight M„ obtained from a reaction of a corresponding monomer selected from a group of lactides, with atleast one catalyst selected from group 4 metal aryloxy compounds M)(0 C6R6)n(OH-R')m mixed in a predetermined feed ratio wherein, M is a metal selected from group 4 of the periodic table , (R) is a first substituent selected from hydrogen, alkyl, halogens and trihalo alkyl; R' is a second substituent selected from alkyl group such as iso propyl and tertiary butyl group; n is a whole number ranging from1-4, and m is a whole number ranging from 0-1. As per the invention the monomer to the catalyst feed ratio is generally of 200:1 molar ratio. In accordance with the invention the number average molecular weight Mn of the polymer is dependent on the feed ratio of the monomer and the catalyst and in particular the molecular weight Mn of the polymer is directly dependent on the feed ratio of the monomer and the catalyst for reaction such that increase in feed ratio of monomer to the catalyst during reaction increases the molecular weight Mn of the polymer. In accordance with the invention the number average molecular weight of the polymer is between 15.58 kg/mol and 135.77 kg/mol and molecular weight distribution is between 1.38 and 1.14.

WE CLAIM:

1. A process for synthesizing a high number average molecular weight Mn
polymer comprising reacting a corresponding monomer from the group of lactides with a catalyst in a predetermined feed ratio characterized in the selected catalyst being a Group 4 metal aryloxy compounds (M)(OC6R6)n(OH-R')m wherein M is a metal selected from group 4 of the periodic table , (R) is a first substituent selected from hydrogen, alkyl, halogens, trihalo alkyl; R' is a second substituent selected from alkyl group such as iso propyl and tertiary butyl group; n is a whole number ranging from 1-4; m is a whole number ranging from 0-1 wherein the feed ratio of the monomer to the catalyst is adjusted to achieve the desired molecular weight Mn of the polymer.

2. The process as claimed in Claim 1, wherein the feed ratio of monomer and the catalyst is generally 200:1 molar ratio.

3. The process as claimed in Claim 1, wherein the feed ratio of the monomer and the catalyst is varied to vary the molecular weight Mn of the polymer.

4. The process as claimed in Claim 1, wherein the feed ratio of the monomer to the catalyst is increased to increase the molecular weight Mn of the polymer.

5. The process as claimed in claim 1 wherein the number average molecular weight of the polymer is between 15.58 kg/mol and 135.77 kg/mol and molecular weight distribution is between 1.38 and 1.14.

6. A polymer having a high number average molecular weight Mn obtained from a reaction of a corresponding monomer selected from a group of lactides, with atleast one catalyst selected from group 4 metal aryloxy compounds M)(OC6R6)n(OH-R')m mixed in a predetermined feed ratio wherein,

M is a metal selected from group 4 of the periodic table ,
(R) is a first substituent selected from hydrogen, alkyl, halogens and trihalo alkyl;

R' is a second substituent selected from alkyl group such as iso propyl and tertiary butyl group;

n is a whole number ranging from 1- 4, and m is a whole number ranging from 0-1.

7. The polymer as claimed in claim 6, wherein the monomer to the catalyst feed
ratio is generally of 200:1 molar ratio.

8. The polymer as claimed in claim 6, has a molecular weight Mn which is dependent on the feed ratio of the monomer and the catalyst.

9. The polymer as claimed in claim 6, wherein the molecular weight Mn of the polymer is directly dependent on the feed ratio of the monomer and the catalyst for reaction such that increase in feed ratio of monomer to the catalyst during reaction increases the molecular weight M„ of the polymer.

10. The polymer as claimed in claim 6 wherein the number average molecular weight is between 15.58 kg/mol and 135.77 kg/mol and molecular weight distribution is between 1.38 and 1.14.