Hierarchical　zeolites　show　great　promise　in　green　chemical　and　petrochemical　processes,　but　their　syntheses　usually　involve　the　use　of　nitrogen-/halogen-containing　templates　whose　removal　from　the　as-synthesized　zeolites　via　calcination　inevitably　leads　to　serious　environmental　pollution,　high　energy　consumption　and　sometimes　destruction　of　zeolite　frameworks.　We　report　an　eco-friendly　and　acid-degradable　polymer　denoted　as　PK3　as　a　multifunctional　template　to　synthesize　single-crystal　hierarchical　zeolites.　It　is　shown　that　by　strongly　interacting　with　zeolite　aluminosilicate　gel　precursors,　PK3　acts　as　a　structure-directing　agent　for　the　nucleation　and　crystallization　of　the　amorphous　gel　into　protozeolite　crystals,　and　via　its　adsorption　on　the　surfaces　of　protozeolite　crystals,　PK3　greatly　inhibits　their　growth　and　thereby　results　in　the　formation　of　zeolitic　nanocrystals.　Furthermore,　these　thermodynamically　unstable　nanocrystals　encapsulating　PK3　spontaneously　aggregate,　then　align　in　an　oriented　manner,　and　at　last　ripen,　leading　to　the　formation　of　single-crystal　zeolite　particles　with　interconnected　mesopores.　Importantly,　the　removal　of　PK3　from　the　as-synthesized　zeolites　can　be　achieved　by　a　simple　acid　treatment.　Thanks　to　these　unique　characteristics　of　PK3,　a　nitrogen-/halogen-free　and　combustion-free　route　is　successfully　achieved　for　synthesizing　hierarchical　MFI,　MOR　and　GME　zeolites.　Moreover,　the　synthesized　MFI　zeolite　exhibits　superior　catalytic　activity　in　cracking　low-density　polyethylene.