Design, Synthesis And Properties Of Side Chain Graft Polyacrylates Containing Liquid Crystal-Poly-L-Lactide

Poly-Lactides and copolymers have attracted much attention due to their huge optical rotatory power and excellent processing property,especially in electro-optical modulation.Poly-L-Lactide(PLLA) can form chiral helical structure due to the presence of a large number of chiral carbon atoms in its main chain.As a result,it can give huge optical rotatory power when uniaxial oriented.Thus PLLA is expected to play an important role in electro-optical modulation as optical elements and optical switching devices.The shortage of its easy-spherulite-froming property of PLLA makes it difficult for the preparation of ordered oriented materials along the helix axis.Liquid crystalline is unique in the ability of self-organization.Hence by combination of the self-organization of liquid crystal groups with PLLA segments can be combined to form molecules with higher ordered materials after treatment,and better optical o properties can be achieved this way.In this paper two types of acrylate including mesogenie units with flexible spacer, AO6OPPO6 and AO6OPCOOPCOO6,and their corresponding homopolymers, P-AOLA_nO6 and P-AOLA_nO6OPPO6 were synthesized.The copolymerization was carried out first between acrylate of mesogenic units and acrylate of Poly-L-lactide AOLA_nO6(n=10,20,30,40) segments.The ¹H NMR results verified the molecular structure of the two types of synthesized target compounds,the acrylate of mesogenic units and their corresponding intermediates and their homopolymers.The PLLA segments were prepared as narrow distribution oligomers(DP=10,20, 30,40) by ring-opening polymerization of lactide using C6OH and HO6OPPO6 as coinitiators and SnOct₂ as initiator,the average molecular weights were monitored by adjusting the corresponding to the feed ratio of Lactide and coinitiators.The PLLA segments were then changed to acrylates by the reaction of OH groups of PLLA with acrylic acid in the presence of N,N'-Dicyclohexylcarbodimide(DCC) and catalyst 4-dimethylaminopyridine(DMAP). Gel permeation chromatography(GPC) was used to characterize the molecular weights and molecular weight distributions of the polyacrylates and copolyacrylates with side chain groups PLLA segments with or without LC units.The results indicated that the polymerization degrees of the copolyacrylates or polyacrylates were about around 10 and with a narrow molecular weight distribution around 1.2. Both of the acrylate esters of mesogenic units show thermotropic liquid crystalline properties:AO6OPPO6(K70.7℃LC84.9℃I) and AO6OPCOOPCOO6(K 42.3℃LC83.7℃I).POM,DSC and XRD results indicated that all the synthesized(co)polyacrylates can form thermotropic liquid crystalline properties,xAO6OPPO6-yAOLA_nO6, xAO6OPCOOPCOO6-yAOLA_nO6,P-AOLA_nO6OPPO6 show thermotropic smectic liquid crystalline behaviors.Circular dichroism(CD) spectroscopy was used to measure the circular dichroism of functional part of PLLA segments in(co)polyacrylates.The positive single circular dichroism absorptions band around 210nm appeared in their CD spectra,both in their solution and bulk films,verify the presence of the helical structure of PLLA segments in polymer materials.The positive absorption bands in CD spectra blue-shifted to 212 nm from 210 nm in solution indictate the paralleled ordering helical chains of PLLA segments in thin solid films.They all showed very huge optical rotatory power and increased around from 1.2 to 1.6 times aider annealing for two hours,indicating the apparent the more ordered orientation of helical segments of PLLA.