Synthesis, Structure, And Property Of Polyolefin/Polyester Diblock Copolymers By A Combination Of Living Polymerization Of Ylides And Ring-opening Polymerization

The Synthesis of block copolymers incorporating polyolefins segments such as polyethylene and more polar segments has always attracted a lot of interest. These copolymers allow to combine the best attributes of polyolefins with original features provided by the other segment such as polarity, functionality, degradability etc. In this article, a new synthesis strategy, the combination of living polymerization of ylides and ring-opening polymerization (ROP), was successfully employed to abtain well-defined polymethylene-b-polymer(ε-caprolactone) (PM-b-PCL) and polymethylene-b-poly(D,L-lactide) (PM-b-PLA) diblock copolymers.Firstly, two hydroxyl-terminated polymethylenes (PM-OH) with different molecular weight and narrow molecular weight distribution were synthesized via living polymerization of ylides with a subsequent molecular oxidation of tris-organoborane using trimethylamine-N-oxide dehydrate (TAO). Subsequently, such polymers were successfully transformed to polymethylene-b-poly(ε-caprolactone) (PM-b-PCL) or polymethylene-b-poly(D,L-lactide) (PM-b-PLA) diblock copolymers by using stannous octoate [Sn(Oct)2] as catalyst for ring-opening polymerization ofε-caprolactone or D,L-lactide.The1H NMR and 13C NMR of PM-OH was indicated the molecular weight and the chain structures. The chain structures of such functionalized polyolefin block copolymers were investigated by GPC and1H NMR. The melting behaviors of the double crystalline diblock copolymers were investigated by DSC. The results indicated that the incorporation of crystalline segments of PCL and PLA chains influence the crystalline process of PM segments greatly, respectively. Porous films were fabricated via the breath-figure (BF) method using different concentration of the PM-b-PCL and PM-b-PLA diblock copolymers in different solvent under a static humid condition, respectively. The LDPE/polyester (such as PCL, polycarbonate, PLA etc) blends were prepared using PM-b-PCL or PM-b-PLA as compatibilizer, respectively. The scanning electron microscopy (SEM) observation on the cryo-fractured surface of such blend polymers indicates that the PM-b-PCL or PM-b-PLA diblock copolymers are effective compatibilizer for LDPE/polyester blends. The results show that:Some internal methyl group (3-4 mol%) on the PM chain occur in the process of living polymerization of ylides. But by the purification of ylides, the content of internal methyl group can be controlled. Using TAO as oxidation, The chain end functionalization efficiency of hydroxyl terminated polymethylenes can reach 100%. PM-OH was were successfully transformed to PM-b-PCL and PM-b-PLA by using stannous octoate as a catalyst for coordination-insertion ring-opening polymerization of s-caprolactone and D,L-lactone, respectively. Both segments of the diblock copolymers can be well controlled by the living polymerization of ylides and the ring-opening polymerization. When the polyester (PCL or PLA) segment introducted to the PM-b-polyester chain, the value of fusing enthalpy changed obviously. The crystalline state of polymethylene was distorted by the incorporation of polyester chain. PM-b-PCL and PM-b-PLA diblock copolymers can be fabricated porous films via the breath-figure (BF) method, respectively. PM-b-PCL and PM-b-PLA are highly effective compatilizer to LDPE/polyester system, respectively, which can effectively improve the surface of two imcompatible materials. Thus blending materials of homogenized and high performance can be obtained.