2-溴丙酰基末端对于PLLA成核行为影响的研究

通过研究2-溴丙酰基单封端的PLLA结晶行为,来探讨聚合物结晶过程中的端基效应.首先通过开环聚合的方法(ROP),以苯甲醇为引发剂,合成了聚(L-乳酸)(PLLA).再将PLLA自由末端的羟基转化为2-溴丙酰基,得到2-溴丙酰基单封端的PLLA-Br.研究表明,2-溴丙酰基末端引入后,聚合物链段运动能力受到抑制,PLL...

NUCLEATION EFFECT OF 2-BROMOPROPIONYL END GROUPS ON CRYSTALLIZATION BEHAVIORS OF PLLA

The crystallization behaviors of single 2-bromopropionyl end-capped poly(L-lactide)(PLLA-Br) were studied to investigate the end group effect during polymer crystallization.PLLA was first synthesized through ring opening polymerization(ROP) using benzyl alcohol as initiator.Then the free hydroxyl end group of PLLA was modified into big rigid 2-bromopropionyl group to obtain PLLA-Br.It was found that PLLA-Br with single 2-bromopropionyl end group possessed higher glass transition temperature than PLLA,indicating that the introduced 2-bromopropionyl end group restricted the chain mobility of PLLA.More interestingly,the 2-bromopropionyl end group greatly affected the crystallization process of PLLA.During non-isothermal crystallization process,the cold crystallization temperature of PLLA-Br was about 12℃ lower than that of PLLA;During isothermal crystallization process after quenching to room temperature,the number of simultaneously growing spherulites(per unit volume) was much higher in the PLLA-Br sample than in PLLA.These results could be attributed to the facilitated nucleation ability of PLLA-Br during cooling process after modification by 2-bromopropionyl end group.Moreover,during isothermal crystallization process directly from melt,both the temperature window for PLLA to form regular banded spherulites and maximum spherulite growing temperature shifted to higher temperature region after end capping,while crystalline structure was identical.This may provide a simple and effective method for PLLA modification to modulate its crystallizability.